The overall objective of this project is to advance the development of a clinically usefully multiplex assay to detect biomarkers of radio-sensitivity that will identify subsets of prostate cancer patients for which radiotherapy should be contraindicated. This assay will be capable of predicting the risk of developing adverse effects ? principally urinary morbidity and rectal injury ? resulting from radiotherapy treatment of prostate cancer. Our studies have identified SNPs in multiple cohorts that are strongly associated with adverse effects resulting from radiotherapy. The goal of the current project is to validate these SNPs in an independent cohort using a multiplex SNP assay. The technical objectives of this project are: (1) Evaluate the clinical outcome associations with all SNPs (p-value < 10-6 in Phase I) in an independent clinical patient set; (2) Expand the content of prototype multiplex assay to detect relevant SNPs discovered in Phase I; (3) Test the ability of the prototype assay to predict adverse outcomes to prostate radiotherapy; and, (4) Obtain quantitative and qualtitative data describing provider preferences for receiving and using genetic information in radiotherapy treatment planning.